What do the terms “heat curing” and “post-curing” mean?
Posted on 7/28/2014
Heat Curing – can be used to accelerate the cure of polyurethane rubbers and plastics, platinum silicone rubbers, epoxy resins and other materials. For example, subjecting a urethane mold rubber mold to mild heat (150 F / 60 C) will reduce the cure time from 16 hours to around 4 hours. Consult product technical bulletin for more information.
Post Curing –
Mold Making – Post curing any mold rubber will enhance the physical and performance properties of the mold rubber. Procedure; following a normal cure cycle for a mold rubber (generally 16 to 24 hours), the cured mold can be exposed to mild heat 150 F / 60 C for 4 to 8 hours.
Platinum Silicone Rubber – can be post cured at higher temperatures to increase the heat resistance of the mold resulting in longer mold life for casting pewter or other metals, for example. Consult product technical bulletin prior to post curing.
Allow the mold rubber to cool to room temperature before using.
Do not use your kitchen oven.
Heat Lamps – can be used but often do not provide even heating. Position as many heat lamps as necessary around the mold or casting to provide even heating. Warning: heat lamps can scorch or burn if not properly used. Use with caution.
Tip: a 100 watt light bulb in a cardboard box may be all that you need to generate enough heat to do the job.
Tip: If you live in a warm climate, you can use the sun to your advantage. Position a broom handle between two chairs and place the mold under the broom handle. Use a colored plastic sheet and make a “tent” over the mold. Area under tent can reach 150 F / 60 C, depending on climate. Caution; use a tarp or covering that does not allow light to pass through to protect your mold against harmful ultra violet (UV) light.
Urethane Plastics – Post curing any urethane plastic will enhance the physical and performance properties of the plastic.
Procedure; flat castings and simple shapes can be post cured outside of mold if placed on a flat surface. 3-d or complicated shapes should be post cured in the rubber mold to prevent distortion.
Following the normal cure cycle for the plastic (consult product technical bulletin), casting can be exposed to mild heat 150°F / 60°C for 2 – 4 hrs. Allow to cool to room temperature before demolding..
Increased Heat Resistance – To give the casting higher heat resistance, cure for two hours at 150°F / 60°C, followed by two hours at 212°F / 100°C. Allow to cool to room temperature before demolding..
Epoxy Resins – Offer the advantage of higher physical and performance properties vs. urethane resins. Epoxy resins also offer higher heat resistance properties. Many epoxy resins require heat curing at a minimum of 212°F / 100°C. For maximum heat resistance, post curing at 300°F / 150°C is recommended. Consult product technical bulletin for complete directions.
Sources Of Heat – What Are Your Options?
An oven is best for applying uniform heating, but use with caution.. We recommend that you do not use your kitchen oven. Mold making and casting should never be done in the home and accidents can happen. For example, applying too much heat to some materials may result in dangerous fumes being emitted and/or a material may melt resulting in a ruined oven.
The FAQ list is offered as a guideline and offers possible solutions to problems encountered during mold making and casting. No warranty is implied and it is up to the end user to determine suitability for any specific application. Always refer to the provided Technical Bulletins (TB) & Material Safety Data Sheets (MSDS) before using any material. A small scale test is suggested to determine suitability of any recommendation before trying on a larger scale for any application.